This invention relates generally to radio frequency phase shifters and more particularly to phase shifters of such type which are adapted for operation in the X-band frequency range from 8.0 to 12.5 GHz.
As is known in the art, radio frequency phase shifters have many applications such as in phased array antennas to collimate and direct a beam of radio frequency energy in a desired direction. One type of phase shifter includes a toroidal shaped ferrite rod disposed in a waveguide, the phase shift of radio frequency energy passing through the waveguide and ferrite rod being in accordance with the magnetic state of the ferrite rod. As is described in an article entitled "Longitudinal Section Mode Analysis of Dielectrically Loaded Rectangular Waveguides With Application To Phase Shifter Design" by G. N. Tsandoulas, D. H. Temme, and F. G. Willwerth, published in I.E.E.E. Transactions on Microwave Theory and Techniques, Vol. MTT-18, No. 2, Feb. 1970, longitudinal section modes (i.e. LSE.sub.1,1, LSM.sub.1,1 and LSE.sub.1,2) may tend to propagate in such a phase shifter. These longitudinal section modes are excited because of discontinuities in the phase shifter, such as minute air gaps (less than tenths of a mil wide) between the ferrite rod and the waveguide walls which are supposedly in contact with each other. One technique suggested in the referenced article for reducing the effect of the longitudinal section modes is to reduce the height of the waveguide. However, at X-band frequencies, the height of the waveguide made according to such suggested technique should not be greater than 0.12 inches. Reducing the height of the waveguide to such a dimension, however, reduces the efficiency of the phase shifter.